The invention relates to an electrophotographic print method for printing a carrier, in which a photosensitive layer system having an electrode layer, an insulating cover layer, and a photoconductor layer arranged between the electrode layer and the cover layer is brought into a homogeneous initial state by impression of an electrical field in a first direction. The photoconductor layer is exposed according to the image through the cover layer or through the electrode layer with predetermined image structures, whereby a second electrical field with an opposed direction is impressed on the layer system so that a charge image corresponding to the image structures arises in and on the layer system. The entire photoconductor layer is subsequently uniformly exposed through the cover layer and/or through the electrode layer, so that a potential image corresponding to the image structures arises on the surface of the cover layer. In a developing step, charged toner particles are subsequently applied to the cover layer, which particles settle according to the potential image as a toner image that is subsequently transferred to the carrier.
The manufacturing of the charge image and of the potential image with the above-named layer system and the steps stated above resembles the method known under the name "Katsuragawa method" "Canon np-process" (cf. e.g. U.S. Pat. No. 3,124,456; DE 1 497 164, or DE 1 522 567). In known print methods of this type, a different image structure can be predetermined from print image to print image. However, with print methods of this type, only print speeds are achieved that lie well below those of offset printing. With an offset printer, up to approximately 2500 print images per minute can currently be printed. However, offset printing has the disadvantage that before printing a print image, a print mask must be prepared inside or outside the offset printer. This results in an expensive print method that works economically only beginning with a number of copies of some hundreds of print images. A rapid change of the image structures is also not possible, and is usually at least on the order of minutes.
In U.S. Pat. No. 4,444,859, electrophotographic methods are explained in which, after exposure according to the image of a light-sensitive layer system, n-copies of the image are printed without the execution of a renewed intermediate exposure. The layer systems, which contain an upper insulating layer, a photoconductor layer and a lower electrode layer, ensure that the photoconductor, which is also mechanically sensitive, is protected by the upper insulating layer during the developing process.
In Patent Abstracts of Japan, vol. 6, no. 195 (Oct. 5, 1982), JP-A-57-105755, an electrophotographic copier is explained that copies at a first speed given an edition n=1, and copies at a speed higher in comparison with the first speed given an edition n&gt;1. The design of the layer system or the influence of the layer system on the print quality is not specified. A technology of n-edition printing is specified in which a toner image is fixed on the photoconductor drum.
DE-A-27 41 713 relates to a method and a means for stabilizing an electrostatic charge image in which the stabilization is achieved by means of the selection of a suitable potential for the production of the charge image.
In U.S. Pat. No. 5,053,304, a layer system is explained for electrophotographic n-edition printing without intermediate exposure.
In U.S. Pat. No. 3,821,931, a copier is explained in which an electrophotographic printer and an offset printer are combined.